Catalytic oxidation of mercaptans



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D. c. BOND CATALYTI OXIDATION OF MERCAPTANS Mw QSN NNEPT Dec. 26, 1950 Filed April 25, 194e Patented Dec. 26, 1950 v'CATALYIIC OXIDATION OF MERCAPTANS Donald C; Bond, Northbrook, Ill., assignor to The Pure Oil Compa-ny, Chicago, Ill., a corporation of Ohio Application April 25, 1946, Serial No. 664,821

3 Claims. 1

This invention relates to a method for removing acidic or mal-odorous sulfur compounds from hydrocarbon fluids and to a method for converting such compounds to sulfur compounds of unobjectionable odor.

The removal of acidic sulfur compounds, such as mercaptans, from hydrocarbon oils by extraction with caustic alkali-methanol solution and regeneration of the resulting solution is disclosed in the patent to Yabroff, No. 2,152,721. The sweetening of hydrocarbon oils by contact with alcoholic alkali solution in the presence oi hydrogen peroxide is disclosed in the patent" to Wilson, No. 2,181,037.

I have discovered' that sweetening of hydrocarbon oils in the presence of alcoholic alkali solution can be readily effected by means of air oxidation if there is present in theA alkali solution a small amount of a phenolic oxidation catalyst. I have also found that the air regeneration of alcoholic alkali solutions used to extract mercaptans and other acidic sulfur compounds from hydrocarbon fluid is greatly accelerated ifa small amount of phenolic oxidation catalyst is present in the alkali solution. The phenolic oxidation catalysts which are used in accordance with my invention are aromatic compounds having one or more hydroxyl groups attached to an aromatic ring and which are oxidizable to the quinone form. The catalyst must be soluble in an effective amount in the alcoholic alkali solution. As compounds which are effective at catalysts may be mentioned, pyroga1lol, butyro pyrogallol, anthragallol, gallic acid, tannicv acid, 3-4-dihydroxy diphenyl, 2-5`dihydroxy` diphenyL butyl' pyrogallol'` and mono methyl ether oipyrogallol. Substanceswhich contain phenolic compounds of the type above pointed out are useful as catalysts. As examples of such compounds may be` mentioned tannin and high-boiling hard` wood tar. As examples of hard wood tar which are particularly effective are U. O. P. Inhibitor No. 1 and I Tar Oil. U. O. P. Inhibitor No. 1 is the commercial designation of a product sold by the. UniversalOil Products Company as a gasoline anti-oxidant. It is a hard wood tar fraction boiling between 240 and 300 C. I Tar Oil is a settled hard Wood tar sold by the Tennessee Products Company; For the method for produc--` ing the settled tars, reference should be had to the article entitled New Products from Wood Carbonization by A. W. Goos and A. A. Reiter of the Cliiis Dow Chemical Company, Marquette,

Michigan, which appeared in the February, 1946 issue of The Journal of Industrial and Engineerhydroquinone, normal ing Chemistry, pages 132 to 135, inclusive. The catalysts are effective when present in the alcoholic alkali solution in amounts of approximately 0.1 to 3% by weight, although we prefer to use an amount equivalent to 1% by weight. In accordance with my invention the alkali solution may be a solution of potassium and/or sodium hydroxide in methyl` and/or ethyl alcohol, preferably with suihcient water present to prevent any substantial amount of alcohol from dissolving in the hydrocarbon undergoing treatment. I have found that the treating solution may contain up to approximately 25% of water without materially affecting the efficiency of the treating or regenerating operation. When Water is present in the treating solution in amounts above 40%, a noticeable decrease in the rateV of oxidation of mercaptans or other acidic sulfur compounds occurs. Where methyl alcohol is used it may be used in substantially anhydrous form, whereas, when using ethyl alcohol, water is preferably present in an amount of not less than 5% to prevent solution of large amounts of alcohol in the hydrocarbon liquid; The amount of alkali in the solution may vary from approximately 5% by weight to an amount suiicient to saturate the solution, although I prefer to use solutions containing between 1`0 and 25% by weight of caustic alkali. Treatment in accordance with my invention is eiected under ordinary atmospheric temperatures. Oxidation proceeds more rapidly at higher temperatures than at lower temperatures, but treating-temperatures above approximately F. should be avoided in'order to obviate the possibility of undesirable oxidation occurring,

The invention will be more readily understood by reference to the accompanying drawings of which Figure 1 is a diagrammatic, elevational view of an apparatus illustrating a method of sweetening hydrocarbon liquid in accordance with my invention, and Figure 2 is a diagrammatic, elevational view of an apparatus useful in removing acidic sulfur compounds from hydrocarbon iiuid in accordance with my invention.

Referring particularly to Figure 1, numeral l indicates a storage tank for holding alcoholic caustic alkali solution for use in the process. The solution will have dissolved therein approximately 1% by weight oi a phenolic oxidation catalyst such as U. O. P. Inhibitor No. 1or I Tar Oil` Suiicient solution is permitted to flow through line 2 into packed tower 3 to fill the tower to the level indicated by line 4. Naphtha is charged from tank 5 through line 6 into the bottom oi tower 3; Air is bubbled into the bottom of the tower 3 through line l. The mercaptans in the naphtha are oxidized to disulfides by the air in the presence of the alcoholic alkali solution containing the catalyst. The sweetened naphtha containing disulfides passes over from the top of the tower 3 through line 8 to the lower portion of a wash tower s. rlhe spent air also passes from tower 3 through line into wash tower il. Water is admitted to the top of the wash tower through line iE in order to wash dissolved alcohol from the naphtha. based on the naphtha is suicient to remove any alcohol contained in solution in the naphtha. The Washed naphtha and spent air pass from the top of the tower il through line i! into finished naphtha tank it?. Spent air escapes from the tank i2 through line i3 and may be further washed with an absorbent such as gas oil or kerosene, if necessary, to remove any hydrocarbon vapors which may be contained therein.

Wash-water leaves the bottom of wash tower 9 through line ld and passes to an alcohol recovery still l5. Alcohol is taken overhead from the still i5 through line i5, condensed in condenser I'! and stored in tank lil. Water leaves the bottom of still l5 through line it. The water leaving still l5 may be used as wash water for charging through line lil. Alcohol from the tank I8 is recycled back to the bottom of tower 3.

Make-up alcoholic caustic alkali solution may be added to the tower 3 from time to time through line 2. Catalyst may be added to the tower from time to time as found necessary through line 20. A withdrawal line 2i is provided at the bottom of the tower 3 in order to withdraw alcoholic alkali solution from time to time as it becomes spent.

The amount of air fed to the tower 3 through line l is regulated so as to allow sufficient air to sweeten the naphtha, but care should be exercised not to bubble air through the tower at such rate or in such amount as to carry excessive quantities of alcohol and hydrocarbon vapors in the spent air.

Referring now to Figure 2, numeral 3o indicates a packed tower into the bottom of which is fed naphtha or other hydrocarbon fluid to be treated through line 3l and to the top of which is fed alcoholic caustic alkali solution through line 32. Line 33 is also provided adjacent the bottom of the tower through which is fed catalyst as required. Treated naphtha leaves the top of the tower through line til and spent alcoholic alkali solution leaves the bottom of the tower through line 35. The naphtha passes from line 34 to the bottom of tower 3S where it is washed with a stream of water which enters the top of the bottom section oi the tower through the spray head 3l. The tower 30 is divided into two sections by the imperforate plate 33. Washed naphtha leaves the top of the bottom section of tower 30 through line 35 and passes to storage. The wash-water containing alcohol washed from the naphtha, leaves the bottom of tower 35 through line 0 and passes to alcohol recovery still di. Alcohol vapors leave the top of the still 4l, pass through condenser and then to receiver titi. Water is withdrawn from the bottom of the still through. line From the receiver lo alcohol is returned through line l5 to settling tank 4t.

The spent alcoholic alkali solution leaving the extraction tower s@ through line passes to the upper portionv of a packed regeneration tower About 1 to 5% by volume of wateri 41. Air is bubbled into the lower portion of the tower 4l' through line t8. rIhe mixture of regenerated alcoholic alkali solution and disuldes leaves the bottom of tower lil through line et and passes to the settling tank it in order to permit the disuliides to settle from the alcoholic alkali solution. The disulfides are withdrawn from the top of settling tank 4S through line e0. The regenerated alcoholic alkali solution together with the alcohol returned from receiver #lll is recycled through line 5l to the upper portion of extraction tower 3d.

Spent air leaves the top of the regenerating tower 4l through line 52 and passes to the lower portion of the upper section of the water-wash tower 35. Vt'ater is sprayed into the upper portion of the upper section of wash-tower 35 through spray-head 53. In this washing operation hydrocarbon vapors and alcohol contained in the spent air are washed therefrom. The wash-water from the upper section of tower 35i passes through line 54 to the spray-head 31 in the lower section of the tower. Where the hydrocarbon undergoing treatment is a relatively high-boiling material, such as naphtha or kerosene, the washing of the spent air in the upper section of tower 36 may be dispensed with. Instead of water, a hydrocarbon absorbent such as gas oil or kerosene may be used to wash the air in the upper section of the tower. In that case the absorbent will be withdrawn through a line (not shown) in the bottom of the upper section of the tower and water fed into the upper portion of the lower section. The water leaving still fil through line lill may be used as wash water in either or both sections oi tower 35. vThe volume ratio of treating solution to hydrocarbon nuid treated may vary from about 1 to 20 to about 1 to 2. With an eiicient contact tower a volume of treating solution equal to about 5 to 10% by volume of the hydrocarbon uid is suicient to remove substantially all acidic sulfur compounds from the fluid.

In the regeneration step sufficient air Vor other free oxygen-containing gas is Abubbled through the used alkali solution to reduce the acidic sulfur content to a point low enough to enable the solution to extract further quantities of acidic sulfur compounds such as mercaptans from the hydrocarbon fluid undergoing treatment, but the amount of air must be limited so that the catalyst is not destroyed by overoxidation or does not exist in the oxidized form at the time the regenerated solution is reccntacted with the hydrocarbon fluid. In order to accomplish these purposes, sufcient air or oxidizing gas is used to reduce the acidic sulfur content of the regenerated alcoholic alkali solution to not less than about .05% by weight and not more than about 0.6% and preferably not more than 0.2% by weight. By permitting the solution after regeneration to stand for a suflicient period of time to reach equilibrium (about 15 to 30 minutes) the solution can be reused without risk of oxidizing mercaptans in situ to any substantial extent, provided a small amount of mercaptan sulfur is still present in the solution.

The rate at which air is bubbled through the used alkali solution should be regulated so as not to carry off excessive amounts of alcohol in the spent air.

An amount of water equal to about 1' to 5% by volume of the naphtha is sufcient to effectively remove alcohol from the spent air and naphtha.

In order to demonstrate the eiiicacy of our invention in regenerating `alcoholic'. alkali 1 solution, .a series `of experiments were performed in `which Avarious .alcoholic alkali `solutions were `used and in which various oxidation catalysts Were used. In this series of experiments `a 50cc. sample of the solution to be tested, `to which hadbeen add- `ed`.1 by weightof the `:catalyst ltobetested and 1% `by `vmeightof sulfur in `the form `of `normal `butyl mercaptan, was placed in a `100 cc. `,graduated cylinder containing 75 `cc. of No. 4 `glass 10 1=beads. A .dip tube was placed in `the rcylinder so that `the bottom thereof `extended Ito the botftomof the cylinder and :air `was passed `through `the tube and bubbled through ,the solution for one hour at the rate of 0.03 cu.ift.perhourzat.a 1

temperature of 75 F. Attheendoi .the-bubbling period the mixture `was `analyzed for `.disuliides in order to determine the amount of mercaptans that was oxidized. The various solutions used in these tests Yand the results obtained are list- .ed in the following Table I.

.from `the Ltable fis that toolhigh concentrations :of alkali `results in 1.a Vlower .rate `oi? oxidation. l(Compare Experiments `6 `and .9 andlalso Experiments t4 .and l0.)

'It will Aalso lbe observed from ,a `comparison :of Experiments 1 `and 8 rthat an 1.excessive ,amount of .water .in the solution reduces lthe rate of .oxi-

\ dation.

'.:In .order to demonstrate the verectiveness of my invention in sweetening :hydrocarbon liquids, Vsour kerosene containing 0.011% by Weight .of mercaptan sulfur was treated in the `following manner: `2*?0 toc. of kerosene and `60 ca .of alcoholic alkali solution to be tested, containing 11% by Weight of the oxidation catalyst to be tested (based on thealkali solution) `were placed in a `pint bottle. The bottle was placed .a `Shak ing machine and wasshaken `at a `ixed rate for sfteen minutes. The :kerosene :and treating so- .Llution were then Vtral'xsierred to a .separatory `.funnel where the `treating solution was l drawn off Table I No. oizExpt, Catalyst Percent KOH Solvent .Oiriln Hydroquinone None Hydroquinone l0 U. .0. P. Inhibitor No. 1 Formula 30 Alcohol ydroquinone. Absolute CZHBQH 32.8 (saturated) Hydroquinone. 10

None 10% NAOH.

Canon 32.5: (saturated) CH OH From the results tabulated in Table I, it Will be seen that the rate of oxidation in which no catalyst was present (Experiments 2 and 13) resulted in a relatively low rate of oxidation. Likewise, the test on an aqueous alkali solution in which catalyst was present gave a low rate of oxidation (Experiment 3). However, when the same alcohol and the same catalyst were combined (Experiment 1) the rate of oxidation was almost twice as great as that which would have been expected from the cumulative results of Experiments 2 and 3.

Another interesting observation which appears and the kerosene was returned to the bottle with a fresh 60 cc. portion of treating solution containing 1% by weight of catalyst. The mixture was again shaken for thirty minutes being flushed with air every ten minutes. If the kerosene was still sour, the treating solution was drawn o as before and a fresh 60 cc. portion of treating solution, containing catalyst, was added and the mixture shaken for thirty :minutes longer with air-flushing every ten minutes.

The data for the various treating solutions and the catalysts used and the results obtained are tabulated in Table II.

Table II Per Cent N o. Alcohol Alkali Alkali Per Cent BSH-S After 15 mln.

After 75 min. shaking After 45 min. shaking shaking do 32.8 U. P. Inhibitor #1....

l0 I Tar Oil l0 U. O. P. Inhibitor #1.... Shghtly Dr. .do

positive.

U. O. I. Inhibitor #1.... 0.0012

ightly Dr. Positiva... dom..

Dr. negative.

Slightly Dr. Positive.

d 0.0012. ..do 10 Pyrogallol.-. 0.0013. Dr. negative. -do... 10 one 0.0045 0.0017

From an examination of TableII, it is evident that I Tar Oil is superior to U. O. P. Inhibitor No. 1 and that U. O. P. Inhibitor No. 1 is superior to pyrogallol as an oxidation catalyst in the sweetening of kerosene in the presence of alcoholic alkali solution. It is also apparent that potassium hydroxide solutions are more effective in the sweetening solution than are sodium hydroxide solutions. The table also demonstrates that too high concentration of alkali has a deleterious effect on the rate of sweetening. By reerring to Experiment No. 16 it will be seen that in the absence of an oxidation catalyst the kerosene could not be sweetened even after 75 minutes of treatment.

It is apparent, therefore, that by carrying out the sweetening operation by means of air or other oxygen-containing gas in the presence of alcoholic alkali solution containing in solution a small amount of phenolic oxidation catalyst, sweetenng of hydrocarbon liquids can be rapidly and eiectively carried out. Regeneration of alcoholic alkali solutions can also be electively carried out by means of air or other oxygen-containing gas if the regeneration is carried out in the presence of a small amount of a phenolic catalyst dissolved in the alcoholic alkali solution. rljhe rate at which regeneration or sweetening can be eiected is far in excess of the rate which would be expected from the cumulative eiect of air regeneration of alcoholic alkali solutions in the absence of phenolic oxidation catalyst and of aqueous alkali solutions in the presence of phenolic oxidation catalysts.

1t is claimed:

1. The method of sweetening hydrocarbon distillatev containing 'mercaptans comprising, intimately contacting said distillate with a solution of alkali metal hydroxide in monohydric .alcohol from the group consisting of methyl and ethyl alcohols, Which solution contains less than 25 per cent by weight of Water, between 10 and 25 per cent by Weight of alkali metal hydroxide from the group consisting of sodium and potassium hydroxide, and about 0.1 to 3 per cent by Weight of a phenolic substance capable of being oxidized to a quinone, while bubbling sufficient air through said distillate to effect sweetening thereof.

2. Method in accordance with claim 1 in which the phenolic substance is a high boiling fraction of hard Wood tar.

3. Method in accordance with claim 1 in which the phenolic substance is settled hard Wood tar.

DONALD C. BOND.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,015,038 Pevere Sept. 17, 1935 2,152,721 Yabroff Apr. 4, 1939 2,181,036 Wilson Nov. 2,1, 1939 2,181,037 Wilson Nov. 21, 1939 2,315,530 Loyd Apr, 6, 1943 2,335,347 McNamara Nov. 30, 1943 2,366,104 Happel Dec. 26, 1944 2,369,771 Bond Feb. 20, 1945 2,390,296 Gilbert Dec. 4. 1945 2,411,105 Nixon et al Nov. 12, 1946 2,413,945 Bolt Jan. 7,1947 

1. THE METHOD OF SWEETENING HYDROCARBON DISTILLATE CONTAINING MERCAPTANS COMPRISING, INTIMATELY CONTRACTING SAID DISTILLATE WITH A SOLUTION OF ALKALI METAL HYDROXIDE IN MONOPHYDRIC ALCOHOL FROM THE GROUP CONSISTING OF METHYL AND ETHYL ALCOHOLS, WHICH SOLUTION CONTAINS LESS THAN 25 PER CENT BY WEIGHT OF WATER, BETWEEN 10 AND 25 PER CENT BY WEIGHT OF ALKALI METAL HYDROXIDE FROM THE GROUP CONSISTING OF SODIUM AND POTASSIUM HYDROXIDE, AND ABOUT 0.1 TO 3 PER CENT BY WEIGHT OF A PHENOLIC SUBSTANCE CAPABLE OF BEING OXIDIZED TO A QUINONE, WHILE BUBLBING SUFFICIENT AIR THROUGH SAID DISTILLATE TO EFFECT SWEETENING THEREOF. 